Over the years, the flight control systems have evolved from simple cable systems, where the pilot had to provide the force to overcome the aerodynamic hinge moments on the control surfaces, to today's fly-by-wire (FBW) systems, where computers signal surface actuators to provide a closed loop maneuver trajectory in response to pilot inputs. Prior to the advent of FBW technology, the flight control systems on commercial airplanes used cables to relay pilot commands to the flight control actuators and/or control surfaces. Even with powered controls, the control system friction was so high that the pilot required a high mechanical advantage on the controls to reduce the effect of the friction, hence the conventional control column and wheel. With the FBW systems, the pilot's inputs are sensed by transducers therefore allowing the use of sidesticks for pilot control input.
In one fly-by-wire architecture, the pilot interfaces with the system through passive sidesticks. With this implementation, no pilot situational awareness is provided through tactile cues such as changes in sidestick feel characteristics. Instead, with passive sidesticks the system has to incorporate hard envelope control limits to prevent the pilot from flying outside the normal flight envelope. This prevents the pilot from using any inherent aircraft maneuver capability in an emergency situation. Because safety is always of the highest priority in the aircraft industry, a system that can provide pilot situational awareness and also provide full aircraft maneuver capability available to the pilot when needed is highly desirable.
Other fly-by-wire systems have been able to provide pilot situational awareness and make the full maneuver capability available to the pilot; however, to accomplish this, the system had to incorporate conventional control columns and control wheels connected to variable feel mechanisms, backdrive servos, trim actuators and other supportive mechanisms. This results in a much heavier and more expensive installation than the use of sidesticks. In addition, sidesticks provide the pilot with an unobstructed view of the instruments and free up valuable space on the cockpit.
The flight control systems used today on all commercial jet transports are exposed to the consequences of a jam in the control system. Some of the systems have incorporated jam override devices that by some pilot action could alleviate a jam. Common to all of these systems is that a jam in the flying pilot's controls would require transfer of control to the other pilot and there would be some small period of time where control inputs are lost. If the jam occurred during the critical part of the flight, such as during take off or final approach, there may not be sufficient time to regain control and prevent a catastrophic event. Therefore, to improve aircraft safety, a need exists to provide continuous control capability from either pilot station following a control system jam.
Examples of active hand controllers are disclosed in U.S. Pat. No. 5,264,768 (Gregory, et al), U.S. Pat. No. 5,347,204 (Gregory, et al), U.S. Pat. No. 5,735,490 (Berthet, et al), U.S. Pat. No. 5,559,415 (Gregory, et al), U.S. Pat. No. 5,489,830 (Fernandez), U.S. Pat. No. 5,291,113 (Hegg, et al) and U.S. Pat. No. 5,694,014 (Hegg, et al).
The system described herein addresses the above issues.